This invention relates to an apparatus for measuring the relative energy consumed during a welding process and, in particular, covers an apparatus to be used as a transducer in connection with a Soudronic welder adapted to weld the longitudinal side seam of a thin metal can body. Soudronic welders for this type of application have a secondary transformer rating of 4 to 8 volts and 5000 amps. The welding is pulse-type at high frequency and can be in the range of 50 to 900 Hz with each alternating waveform producing a power pulse. A travelling electrode being a copper wire is positioned between the surfaces to be welded and the output terminals of the secondary winding for the welding transformer. The copper wire is used between each of the electrodes and the metal surface to be welded and is moved after each welding pulse in order to prevent deterioration of the welding electrodes.
Can bodies are generally hollow cylindrical constructions which are formed along a longitudinal edge into a closed cylinder leaving both ends open. The meeting edges of the cylinder thus formed from a flat blank of material are overlapped for purposes of welding. The blanks are preferably fashioned from preprinted (lithography) tinplate or tin free steel chrome-type such as MRT3 having a 0.25 ETP on the surfaces. Such material can range from 65 to 112 pound plate weight ber base box which represents a range of 0.007" to 0.0123" in thickness depending upon the application of the container to be formed from the tinplate and/or tin free steel chrome-type. A welded side seam is preferable to other forms of side seams such as a soldered can seam or a glued together joint. More particularly, in aerosol containers which must be capable of withstanding up to 200 pounds per square inch of internal pressure, a welded longitudinal side seam has a great many advantages. Similarly, in containers which are of a particular configuration which is too large to be drawn (as, for example, a two-piece container is), a welded side seam gives the requisite strength and simplifies the manufacture of such containers as they are too long or too large for drawing. In other applications it is important to have lithograph information on the exterior surface of the containers. Quality lithography cannot be applied at high-speed to a preformed drawn container so a container with a manufactured side seam is required.
Hall effect devices have been used in connection with a number of transducer applications some of which have been applied to welding machines see, for example Noth U.S. Pat. No. 3,240,961; Hill U.S. Pat. No. 3,194,939; Barnhart et al U.S. Pat. No. 3,335,258 and Treppa et al U.S. Pat. No. 3,389,239. Each of the foregoing is designed to use a Hall device in combination with a welder for purposes of current determination. Similarly, the Hood U.S. Pat. No. 3,365,665 shows a Hall transducer which has been used in a system for measuring current flow in high voltage conductors e.g. power lines. The Hood patent is particularly interesting in that the problems wrought by temperature changes are recognized and correction is made for Hall gain versus temperature. The circuit of Hood does not automatically compensate for the Hall DC offset versus temperature at zero magnetic field. The mentioned prior art patents use the Hall effect device to sense varying magnetic fields during weldings. Hood also recognizes that such devices are sensitive to current and voltage input as well as ambient temperature, but such outside influences can be adjusted to be respectively small with respect to the signal put out by the Hall effect transducer in connection with the application disclosed in the prior art.
In a high-speed operation such as welding thin metal can bodies at several hundred per minute with an alternating current welder, the influences of input current and voltage as well as ambient temperature becomes significant when one is trying to measure small changes in the welder operating conditions. It is, therefore, the function of the circuit herein to completely compensate for the aforesaid conditions in an effort to provide a Hall effect transducer which will be useful in monitoring the energy used to weld the side seam of a thin metal container and same will be set forth in the following summary.